According to the application of two step ladder-shaped propellant in solid rocket motor, a numerical simulation was made for the type of solid rocket motor ignition characteristics of interior flow field. The FLUENT software was used to make unsteady two-dimensional axisymmetric numerical simulation, through the UDF programming, the cell surface critical criteria were applied to achieve the surface cells in different parts of the gas increases quality respectively, pressure distribution and variation in different regions of chamber and shock wave transmission near the igniter nozzle were obtained. The result can predict the characteristics of ignition flow field, and provide basis for the ignition study and design of ladder-shaped propellant solid rocket motor.